The overall objectives of the project are to examine the role that catheptic proteases and other acid hydrolases play in the turnover of specific cellular enzymes and proteins during the synchronous cell cycle of the unicellular eukaryote Chlamydomonas reinhardtii. Apart from ascertaining the function of multiple forms of cathepsin D known to occur in this organism, other lysosomal enzymes will be isolated and purified, and their ability to degrade specific proteins and nucleic acids studied. Lysosomal vesicles will be isolated from different stages of cell development and their hydrolytic enzyme content assayed. The transport of substrates into these vesicles and the degradation of natural purified protein substrates will be studied.